Monte Carlo MCNP-4B-based absorbed dose distribution estimates for patient-specific dosimetry

This study was intended to verify the capability of the Monte Carlo MCNP-4B code to evaluate spatial dose distribution based on information gathered f rom CT or SPECT, Methods: A new: three-dimensional (3D) dose calculation ap proach for internal emitter use in radioimmunotherapy (RIT) was developed u sing the Monte Carlo MCNP-4B code as the photon and electron transport engi ne. It was shown that the MCNP-4B computer code can be used with voxel-base d anatomic and physiologic data to provide 3D dose distributions. Results: This study showed that the MCNP-4B code can be used to develop a treatment planning system that will provide such information in a time manner, if dos e reporting is suitably optimized. If each organ is divided into small regi ons where the average energy deposition is calculated with a typical volume of 0.4 cm(3), regional dose distributions can be provided with reasonable central processing unit times (on the order of 12-24 h on a 200-MHz persona l computer or modest workstation). Further efforts to provide semiautomated region identification (segmentation) and improvement of marrow dose calcul ations are needed to supply a complete system for RIT. It is envisioned tha t all such efforts will continue to develop and that internal dose calculat ions may soon be brought to a similar level of accuracy, detail, and robust ness as is commonly expected in external dose treatment planning. Conclusio n: For this study we developed a code with a user-friendly interlace that w orks on several nuclear medicine imaging platforms and provides timely pati ent-specific dose information to the physician and medical physicist. Futur e therapy with internal emitters should use a 3D dose calculation approach, which represents a significant advance over dose information provided by t he standard geometric phantoms used for more than 20 y (which permit report ing of only average organ doses for certain standardized individuals)